Petrogeochemistry And Geological Significance Of Middle Jurassic Granite In Qingyuan Area, Liaodong

Through petrogeochemistry,zircon U-Pb geochronology in Huangniling and Gouniandian pluton from the northeastern margin of North China,it provides a new evidence for the time of the transformation between the Paleo-Asian tectonic domain and the marginal Pacific tectonic domain by discussing the petrogenesis and tectonic setting of the rock mass.It is indicated that the Huangniling pluton is composed of pyroxene adamelite,and it formed during the early Middle Jurassic with a weighted mean age of 174.4 Ma.And the Gouniandian pluton is composed of two mica granodiorite,it formed during the early and middle periods of Middle Jurassic with a weighted mean age of 170.9±0.55Ma.The major elements of the adamellite are characterized by high Al,Ca,Na,Fe and low Mg,with negligible Eu anomalies.Huangniling pluton is enriched in large ion lithophile elements?LILE??e.g.,Rb,Sr,Ba,K?and high field strength elements?LREE?,and depleted in high field strength elements?HFSE??e.g.,Nb,Ta,Zr,Hf,Ti and HREE?and compatible element V,Cr,Co,Ni.The adamelites in Huangniling belongs to C-type Adakite with high Sr and low Yb.?_Hf?t?=-12.77^-15.93,T_DM2=2028²227Ma.The major elements of the two mica granodiorite are characterized by high Si,Al and low Ca,Na,Fe,Mg,with negligible Eu in middle negative anomaly.Gounaidian pluton is enriched in large ion lithophile elements?LILE??e.g.,Rb,Ba,K?and high field strength elements?LREE?,but depleted in large ion lithophilic elementsand?e.g.,Sr?,and depleted in high field strength elements?HFSE??e.g.,Nb,Ta,Zr,Hf,Ti and HREE?and compatible element V,Cr,Co,Ni.The adamelites in Huangniling belongs to C-type Adakite with high Sr and low Yb.?_Hf?t?=-10.18^-13.88,T_DM2=1746Ma²096Ma.The C-type Adakite Huangniling pluton magma was derived mainly from partial melting of mafic rocks in thickened lower crust.The Himalaya-type Gounaidian pluton magma was derived mainly from partial melting of metamudstone in upper crust.Since the Middle Jurassic,the control of the Paleo-Asian ocean tectonic system on the study has ended.The circum-Pacific tectonic system dominates the structural magmatism in this area.The depth of C-type Adakite magma source region is more than 50 km,and that of Himalaya-type granite is 40⁵0 km.The C-type Adakite Huangniling pluton and Himalaya-type Gounaidian pluton coexist in space,it is indicated that the earth crust became thinner and the tectonic setting changed from compression to extension from174 Ma to 170.9 Ma.